By default Photo Mechanic displays the embedded JPEG for standalone RAW files and displays the JPEG when RAW and JPEG files are combined into one thumbnail. Unless Camera Raw updates the embedded JPEG in the RAW file (which I don't think any software actually does), then the embedded JPEG is going to remain black and white.
When you Enable RAW Rendering, then the image that you'll see in Photo Mechanic is the embedded JPEG from the DNG that Adobe DNG Converter creates (the DNG is thrown out after it is created and the JPEG extracted). What that JPEG looks like is entirely up to how Adobe DNG converter interprets the raw data. That said, one of my colleagues grabbed a sample file with a black and white film simulation and when I enable RAW rendering, it shows the image in color. My guess is that you have the RAW and JPEG combined into one thumbnail, so it skips even attempting to render the DNG, because it's showing the JPEG.
>Also in the Render Cache the option " BUILT IN REnder" is greyed out. Is that normal.
Yes.